Electrostatic spray coating apparatus

ABSTRACT

Apparatus for applying a shave facilitating coating to razor blades includes a chamber for holding the coating material and an aspirator for aspirating the coating material to form a mist of fine particles within the chamber. The chamber has a relatively large outlet port so that the mist of particles issue through the outlet port at a low velocity. The particles are then accelerated in an electrostatic field and are deposited on the sharpened edges of the razor blades in a uniform film having a thickness in the order of 2000 A. or less.

United States Patent Inventor Frank Hamilton Fish 2,847,248 8/1958 Schmitt et al 239/338 Westwood, Mass. 2,951,644 9/1960 Mahon etal.... 239/338 X Appl. No. 786,318 3,049,301 8/1962 Heuschkel 239/15 Filed Dec. 23,1968 3,206,175 9/1965 Boteler i. 239/338 X Patented June 29,1971 3,498,541 3/1970 Taylor, Jr. et a1 239/15 Asslgnee gz g at Primary Exarm'nerMv Henson Wood, Jr.

Assistant ExaminerMichael Y. Mar

Attorney-Willis M. Ertman ELECTROSTATIC SPRAY COATING APPARATUS 8 Claims, 4 Drawing Figs.

U.S. Apparatus for a shave facilitating coat. 239/338, 239/601 ing to razor blades includes a chamber for holding the coating Int. Cl B05!) 5/02 material and an aspirator f aspirating the coating material to 0 Search 5, 3, form a mist of fine particles within the chamber The chamber 302,311 599, 601 has a relatively large outlet port so that the mist of particles R f Clad issue through the outlet port at a low velocity. The particles e I are then accelerated in an electrostatic field and are deposited UNITED STATES PATENTS on the sharpened edges of the razor blades in a uniform film 2,819,716 1/1958 Miller 239/338 X having a thickness in the order of 2000 A. or less.

1 s 6 3 \1 it 50 3 .i HI lr T 2 22 1 1' d l I ll I l l 58 56 54 q l l I x l I \l l I i m T l6 M VOLTAG E H i 1 SOURCE ELECTROSTATIC SPRAY COATING APPARATUS SUMMARY OF INVENTION This invention relates to electrostatic spray coating apparatus for the application of coating materials to provide a coating on a surface and more particularly to apparatus particularly useful for placing a shaving facilitating coating on the cutting edges of razor blades during the manufacturing operation.

In present razor blade technology, it has been found that fluorocarbon materials, when properly applied to the shaving edge of the razor blade, significantly improved the shavability characteristics of the razor blade. A thin uniform coating over the entire surface of the final facet is desired, which coating can be obtained by spraying the coating material in a uniform distribution of extremely fine particles that are deposited with liquid. A particularly advantageous coating material for such an application is an aqueous dispersion of a fluorocarbon telomer and it is a particular object of this invention to provide novel and improved apparatus for applying a thin uniform coating of such material to the sharpened edges of razor blades in a production process.

Another object of the invention is to provide novel and improved apparatus for applying coating material to the sharpened edges of razor blade elements economically and at a rate consistent with present day mass production requirements, which apparatus are capable of operating automatically with minimum amount of supervision and maintenance while assuring a product of high quality and uniformity.

A further object of the invention is to provide novel and im proved apparatus for applying coating materials through the use of electrostatic techniques.

Another object of the invention is to provide novel and improved apparatus for applying a telomer material in thin coatings of uniform coverage efficiently and economically.

In the practice of the method of the invention with this system, after establishment of an electrostatic field having an average gradient in the range of 49 kilovolts per centimeter between a workpiece support and a mist generator, and a quiescent atmosphere adjacent the workpiece support, particles of the coating material less than microns in size are continuously generated for acceleration under the influence of the electrostatic field for impact on the surface to be coated. Relative movement between the surface to be coated and the mist generator is produced at a continuous and uniform rate and a coating material is deposited and produces a coating which covers the entire surface to be coated. The surface to be coated in particular embodiments is preheated as a function of the coating material. Such preheat is desirable for slow drying dispersants to speed the drying of drops on the edge of a blade so that the solids are deposited uniformly and dry sufficiently rapidly to avoid coalescing of the drops and formation of a bead of solid material along the facet of the blade away from the ultimate edge and yet not dry so fast that spots of solids are scattered with bare spaces between them. Freon 1 l3 dispersions have been found to require no preheat, satisfactory results have been obtained with 4 percent aqueous dispersions with a 150 F. preheat, and one-half percent aqueous dispersions with drops of less than lO-micron size preferably are used with a 205 F. preheat at a blade move ment rate of 50 cm./min. and dispersion consumption rate of 1 l0 cc./hr.

The outlet port of the mist generator is preferably so spaced from the blade edges (the surface to be coated) that the angular difference between the length of the outlet port and the length of the blade edge is less arc-tan 0.1 so that the particles of coating material are accelerated by the electrostatic field along generally parallel paths from the outlet port to the blade edges. In such a system the particles are introduced into the electrostatic field at low velocity, preferably less than 2 meters per second. This geometry of material movement provides a uniform and efficient deposition of material on the blade edges.

A razor blade coating system constructed in accordance with the invention includes a workpiece transport for a stack of blades, the blades in the stack being disposed in face to face relation with their sharpened edges aligned and exposed to the coating source. The system also includes an aspirating system for generating a mist of coating material in which the particles have a size of less than 10 microns, this mist generator producing an output of low velocity particles and including an outlet passageway of relatively large cross-sectional area. The mist generator and the workpiece support are electrically insulated from ground and are connected in electric circuit to establish an electrostatic field of magnitude in the range of 49 kilovolts per centimeter and preferably about 5 kilovolts per centimeter. The mist generator and the workpiece support structure are movable relative to one another so that the workpiece may be moved past the outlet passage of the mist generator while the output mist is accelerated under the influence of the electrostatic field for impingement on the edge surface to be coated.

In a particular embodiment for the coating of razor blades, the system further includes apparatus for heating the blade prior to the application of the coating material. The mist generator in that embodiment includes an outlet passageway having an elongated inclined surface on which larger particles impinge and are removed from the output particle stream and an outlet port structure of electrically insulating material, the port being of horse-collar configuration and having a plane surface disposed parallel to the blade edges to be coated.

While this apparatus provides a particularly convenient and efficient method of applying a coating material to the shar pened razor blade edges as a shave facilitating coating it may be practiced with a variety of workpiece surfaces and with a variety of coating materials including electrolytes. It is particularly useful in applying an aqueous dispersion of a fluorocarbon telomer to provide a shave facilitating film of thickness in the order of 2000 A. or less on the sharpened edges of razor blades, which blades exhibit excellent shaving characteristics.

Other objects, features and advantages of the invention will be seen as the following description of particular embodiments of the invention progresses, in conjunction with the drawings, in which:

FIG. I is a sectional view of apparatus employed in the practice of the invention;

FIG. 2 is an enlarged view of the aspirator structure employed in the mist generator shown in FIG. I;

FIG. 3 is an end view taken along the line 3-3 of FIG. 1 of the configuration of the output channel of the mist generator; and

FIG. 4 is a diagrammatic top view of an arrangement of a furnace and mist generators in a system constructed in accordance with the invention.

DESCRIPTION OF PARTICULAR EMBODIMENT With reference to FIG. I there is provided a mist generator structure and a workpiece support 12 on which a stack of razor blades 14 is supported. The mist generator includes a glass chamber 16 which holds a supply of the coating material 18, in this case an aqueous dispersion of a tetrafluoroethylene polymer. Disposed on the supply tank is a nickel plated brass chamber cap and aspirator structure 30. The supply chamber cap structure has an outlet port 20 of 4 square centimeters cross-sectional area, the base of which is disposed l2 centimeters above the base of chamber 16. An outlet tubular passage 22 connected to port 20 has an extension 24 of polypropylene (of oval or horse-collar" cross-sectional configuration as indicated in FIG. 3) mounted thereon. The total length of passage 22 and extension 24 is 6 centimeters, its height is 2.7 centimeters and its width (at its widest point) is 1.7 centimeters. The workpiece support 12 is disposed so that the center of the blades M is in alignment with the axis of passage 22.

The aspirator structure 30 includes a tubular body section 32, at the top of which is supported a vertically adjustable output regulator plate 34. The bottom of tube 32 is open to the supply chamber 16. Disposed in tube 32 is an aspirator assembly 36, details of which may be seen with reference to H0. 2. That assembly includes an outlet port 40, an air supply passage 42, and a fluid supply passage 44. Jet passage 46 (0.5 mm. in diameter) connects the air supply passage 42 to the outlet port 40 and jet passage 48 (0.5 mm. in diameter) connects the fluid supply passage 44 to outlet port 40. Passage 44 is connected to fluid tube 50 which extends through the upper wall of chamber 16 to the bottom thereof. Air inlet passage 42 is connected to tube 52 which is connected through a filter 54 and a pressure regulator 56 to a source of compressed air 58. Air under pressure (suitable pressure being in the range of l8-30 p.s.i.) is applied to passage 42 and aspirates the coating material from container 16 for dispersion in a mist downwardly through tube 32, together with air drawn in through the port below regulator plate 34. The heavier aspirated particles are all returned to the supply of the coating material 18 while the smaller particles flow upwardly and through outlet port 20 and the inclined passage 22 for discharge at low velocity (in the order of l meter per second) into the atmosphere. The inclined surface of passage 22 cl lects particles of intermediate size and returns those particles to chamber 16 so that only particles of less than microns in size are dispersed into the air.

Mists of a variety of coating materials may be generated with this apparatus, including solids such as telomers as dispersions in water, alcohols, freons, or various fluorocarbon liquids. A preferred coating material is an aqueousdispersion of tetrofluoroethylene telomer of the type disclosed in the copending U.S. application Ser. No. 765,693 which was filed Oct. 7, 1968 in the name of Fischbein et al. Operation of this mist generator consumes that coating material at the rate of approximately 135 cubic centimeters per hour, of which about 25 cubic centimeters is due to loss of water by evaporation.

A high voltage power supply 60 (in a particular embodi merit a Spellman Model 2040 power supply which has a variable output with a range of 040 kv. at l milliampere current) is connected with its positive terminal grounded and connected to the blade support structure 12 and its engativc terminal connected to the nickel plated brass aspirator structure 30. The container 16 is supported on an electrical insulator. The blade support is positioned relative to container 16 so that the sharpened edges of the blades 14 are 7% centimeters from the container body and a voltage gradient of 5.33 kv. per centimeter is established. The angular difference (FIG. 1) between the length of the outlet port 24 and the length of the razor blades 14 (3.7 cm.) with this spacing is arc-tan 0.067.

With reference to FIG. 4, an enclosure 70 is provided in which six mist generators 10-1l06 are disposed. A blade transport structure, which includes a rail 72 and a chain 74 driven by a variable speed reversible motor mounted outside of enclosure 70, supports a series of blade holders 12 in the form of knives which run through the central slots in the blades. Typically, there are 600-1200 blades in each stack and a lava spacer 76 is used to separate the blades from the clamps 78 mounted on each knife 12. Adjacent enclosure 70 is an oven 80 through which the blade transport passes. in this embodiment, the blades are heated to a temperature of 205 F. prior to entry into enclosure 70.

In operation, the aqueous dispersion 18 is placed in chamber 16 preferably only half full to minimize the influence of foaming and liquid entrainment on the formation of mist. The electrostatic field is established and mist is generated while the blade transport is advanced through enclosure 70 at a rate of 50 centimeters per minute past the six mist generators 10 so that a fluorocarbon coating in the thickness range of 2000 A. is deposited on both edges of the blades. This disper sion is consumed at a rate of about 660 cc./hour. The blades are then heated to cure the coating material. Razor blades with coatings applied by this method and apparatus compare favorably from the standpoint of product uniformity and economy, as well as shaving characteristics, with commercially available razor blades that have been coated with other spray techniques.

While a particular embodiment of the invention has been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What I claim is:

1. Apparatus for electrostatically spray coating an article comprising a chamber for holding spray coating material in liquid form,

an aspirating device for aspirating said coating material to form a mist of particles within said chamber,

said chamber having an outlet port of sufficient size so that particles of coating material ofa size less than 10 microns will be issued through said outlet at low velocity, said particles providing on deposition a spot size not greater than in the order of 40 microns in diameter, an elongated passageway attached to said output port, said passageway having a cross-sectional area greater than 1 square centimeter and including an extension of electrically insulating material whose upper portion is of smaller width than its lower portion, said extension having an outlet surface defining a plane parallel to the surface to be coated; and a high voltage power supply connected to said mist generator for providing an electrostatic field having an average gradient in the range of 40008000 volts per centimeter extending between said mist generator and the article to be coated electrostatically to effect deposition on the article of a substantial portion of the mist particles with which portion would not otherwise have been deposited thereon.

2. The apparatus as claimed in claim 1 wherein said mist generator includes aspirator structure mounted in an clongated vertically disposed tubular structure for discharging a mist of particles downwardly through said tubular structure for impingement on the surface of the supply material dispensed in said supply chamber.

3. The apparatus as claimed in claim 1 wherein said high voltage power supply provides a voltage gradient of about 5000 volts per centimeter.

4. The apparatus as claimed in claim 1 wherein the angular difference between the length of said outlet port and the length of the surface to be coated is less than arc-tan 0.1.

5. The apparatus as claimed in claim 4 wherein said passageway is inclined at an angle of at least about 10 and said passageway is of oval configuration at its outlet end.

6. Apparatus for electrostatically spray coating an article comprising a chamber for holding spray coating material in liquid form,

an aspirating device for aspirating said coating material to form a mist of particles within said chamber,

said chamber having an outlet port of sufficient size so that particles of coating material ofa size less than l0 microns will be issued through said outlet at low velocity, said par ticles providing on deposition a spot size not greater than in the order of 40 microns in diameter, the angular difference between the length of said outlet port and the length of the surface to be coated being less than arc-tan 0.1, an elongated passageway attached to said output port, said passageway having a cross-sectional area greater than 1 square centimeter and including an extension of organic material whose upper portion is of smaller width than its lower portion, said extension having an outlet surfacc defining a plane parallel to the surface to be coated, said passageway being inclined at an angle of at least about 10 and said passageway being of oval configuration at its outlet end; and a high voltage power supply connected to said mist generator for providing an electrostatic field having an average gradient in the range of 40008000 volts per centimeter extending between said mist generator and the article to be coated electrostatically to effect deposition on the article of a substantial portion of the mist particles with which portion would not otherwise have been deposited thereon. 7. The apparatus as claimed in claim 6 wherein said mist generator includes aspirator structure mounted in an elongated vertically disposed tubular structure for discharging a 

2. The apparatus as claimed in claim 1 wherein said mist generator includes aspirator structure mounted in an elongated vertically disposed tubular structure for discharging a mist of particles downwardly through said tubular structure for impingement on the surface of the supply material dispensed in said supply chamber.
 3. The apparatus as claimed in claim 1 wherein said high voltage power supply provides a voltage gradient of about 5000 volts per centimeter.
 4. The apparatus as claimed in claim 1 wherein the angular difference between the length of said outlet port and the length of the surface to be coated is less than arc-tan 0.1.
 5. The apparatus as claimed in claim 4 wherein said passageway is inclined at an angle of at least about 10* and said passageway is of oval configuration at its outlet end.
 6. Apparatus for electrostatically spray coating an article comprising a chamber for holding spray coating material in liquid form, an aspirating device for aspirating said coating material to form a mist of particles within said chamber, said chamber having an outlet port of sufficient size so that particles of coating material of a size less than 10 microns will be issued through said outlet at low velocity, said particles providing on deposition a spot size not greater than in the order of 40 microns in diameter, the angular difference between the length of said outlet port and the length of the surface to be coated being less than arc-tan 0.1, an elongated passageway attached to said output port, said passageway having a cross-sectional area greater than 1 square centimeter and including an extension of organic material whose upper portion is of smaller width than its lower portion, said extension having an outlet surface defining a plane parallel to the surface to be coated, said passageway being inclined at an angle of at least about 10* and said passageway being of oval configuration at its outlet end; and a high voltage power supply connected to said mist generator for providing an electrostatic field having an average gradient in the range of 4000-8000 volts per centimeter extending between said mist generator and the article to be coated electrostatically to effect deposition on the article of a substantial portion of the mist particles with which portion would not otherwise have been deposited thereon.
 7. The apparatus as claimed in claim 6 wherein said mist generator includes aspirator structure mounted in an elongated vertically disposed tubular structure for discharging a mist of particles downwardly through said tubular structure for impingement on the surface of the supply material dispensed in said supply chamber.
 8. The apparatus as claimed in claim 7 wherein said high voltage power supply provides a voltage gradient of about 5000 volts per centimeter. 